Physical Sciences, Inc. (PSI), in collaboration with The Forsyth Institute, Cambridge, MA proposes to investigate the use of combined Raman microspectroscopy-Optical Coherence Tomography (OCT) imaging for in vivo diagnosis of tooth decay, cracks, and periodontal diseases. Both Raman and OCT are powerful technologies with proven success in human tissue diagnosis while avoiding the need for ionizing radiation exposures. While Raman microspectroscopy is used to discriminate between different species of bacteria grown in biofilms, such as Streptococcus sanguinis and Streptococcus mutans, which are major components of the oral plaque, OCT allows for visualizing soft tissue inflammations, as well as tooth decay and cracks. Therefore, the complementary capabilities of these two optical technologies may be exploited to offer a clinically comprehensive set of parameters for more reliable diagnosis of oral health status. Thus, this technology could help clinicians to provide more reliable diagnosis of dental lesions by assisting them in better selecting areas that need immediate treatment. For a preliminary investigation of this powerful dual-mode imaging approach, a novel method for combining these two imaging modalities into a hand-held probe is proposed. In Phase I we propose to investigate the use of Raman and OCT within the same optical layout and preliminarily test this dual imaging approach ex vivo on excised tissue specimens. Based on Phase I conclusions, both the instrument and the hand-held probe will be improved in Phase II and tested at Forsyth on patients with oral biofilm degradation and tooth cracks or decay.